Fresnel lens with variable draft angle

Abstract

A Fresnel lens with Fresnel prisms having a first facet, called the main facet, and a second facet, called the draft facet, the draft facet making a draft angle to the optical axis, the draft angle being variable along at least one Fresnel prism, so that the draft angle is higher on one side of the lens than on the other.

What is claimed is: 
     
       1. A Fresnel lens having an optical axis and comprising Fresnel prisms, each Fresnel prism having a first refracting facet, called the main facet, and a second reflecting facet, called the draft facet, the draft facet making a draft angle with respect to the optical axis, wherein for at least one of the Fresnel prisms, referred to as the variable-draft-angle Fresnel prism, the draft angle is variable, so that the draft angle is higher on a first side of the Fresnel lens than on a second side of the Fresnel lens that is substantially opposite the first side, wherein
 along the at least one of the variable-draft-angle Fresnel prisms and from the second side to the first side, the at least one of the variable-draft-angle Fresnel prisms comprises at least one spreading segment located laterally with respect to a direction transverse to the optical axis, and extending from the first side to the second side, and in the spreading segment, 
 the draft angle gradually increases from the top of the second side to a start of the spreading segment, then gradually decreases to an end of the spreading segment, and then gradually increases to the bottom of the first side. 
 
     
     
       2. The Fresnel lens according to  claim 1 , wherein the angle between the start and end of the spreading segment and the vertex of which is substantially on the optical axis has a value between 15° and 45°, the angle extending on either side of a point located halfway between the first side and the second side. 
     
     
       3. The Fresnel lens according to  claim 1 , wherein
 the Fresnel lens is oriented, in a vehicle, with the first side at the bottom of the Fresnel lens and the second side at the top of the Fresnel lens.